The membrane changes involved in the developmentally programmed decrease in cell adhesiveness that accompanies sea urchin embryo primary mesenchyme formation are being subjected to continued biochemical analysis. Specific projects in progress include: 1. Micromere isolation and differentiation of primary mesenchyme in vitro. 2. Analysis of a number of cellular events that occur during reaggregation of isolated micromeres. 3. Lectin agglutinability of developing primary mesenchyme cells. 4. Identification of lectin receptors on developing primary mesenchyme cells. 5. Galactose oxidase labeling of intact developing primary mesenchyme cells.